Legend of Spyro, as well as Skylanders, are reboots of the Spyro series. Legend of Spyo was met with mixed reception, but the general consensus is that it's overall worse than the original PS1 trilogy, and even the GBA trilogy. Skylanders is its own thing arguably, Spyro was just shoehorned in to revive the IP while attracting the fans I suppose, Skylanders is actually pretty good and different though, a reboot done right I think.
Enter The Dragonfly is to the Spyro series what Wrath of Cortex was for the Crash Bandicoot series, that is to say the first "next-gen" entry that unfortunately had some technical issues to it. While Wrath of Cortex merely suffered from long load times(Which were fixed in the Xbox and Gamecube releases), Enter The Dragonfly suffered from many more glitches unfortunately; It was rushed to meet the holiday deadline in 2002, and it shows. Despite the glitches, Enter the Dragonfly is still playable, but just barely. It follows the format of the PS1 trilogy, but it offers much less in the way of levels; I recall only 9 separate worlds, 10 including the hub world. It introduces elemental breaths and the wing shield, but those mechanics weren't perfected until the next entry. If you want to play Enter The Dragonfly, it is recommended to go with the Gamecube version as it's somewhat less glitchy for the most part.
A Hero's Tail is like the Crash Twinsanity of the Spyro series. It takes the PS1 formula and advanced it, while taking some elements from Enter The Dragonfly. Developed by the same people behind Crash Bash, A Hero's Tail is the best Spyro of the GCN/PS2/Xbox generation. It has virtually no glitches, and advanced the formula. Even though each world only has two major levels to it, those levels take a while to complete, especially 100%. There is still backtracking which was present in Ripto's Rage and Year of the Dragon, but it's toned down to a degree thankfully. Spyro retains his moves from the PS1 trilogy, such as Headbashing, and also has the elemental breaths and wing shield from Enter The Dragonfly. Like Year of the Dragon, it offers several playable characters;
Sgt. Byrd takes over for the "Flight" and "Speedway" sections of the game, while Hunter takes on specialized situations in the game that require his cheetah abilities and archery, he even gets his own level late in the game. Blinx the Mole is the new character, who gets his own underground sections throughout the game. Sparx is also his own character; His sections play like a rail shooter.
Hero's Tail also has some fan service, though it's fairly light. If you enjoyed Spyro the Dragon, you'll appreciate who the first boss is we'll just say... but overall, I enjoyed A Hero's Tail much more than Enter The Dragonfly.
The GBA games are isometric platformers, and for the most part they work, but overall they don't innovate nearly as much as the PS1 trilogy. Still, it's handheld Spyro done right, much like Crash Bandicoot The Huge Adventure and N-Tranced were handheld Bandicoot done right.